Fluid-to-electrical transducer



Jun 29,1965 VWQMGWADEYI 3,192,470

FLUID-TO-ELECTRIGAL TRANSDUCER Filed July 16, 1962 I FIG. I

UTILIZATION CIRCUIT SIGNAL SOURCE FIG.4

II I9 23 2| 3 '3 INVENTOR.

mm! a um 3y ATTORNEYS United States Patent 7 3,192,470 FLUID-TO-ELECTRICAL TRANSDUCER Walter G. Wadey, Bethesda, Md., assignor to Sperry Rand Corporation, New York, N.Y., a corporation of Delaware Filed July 16, 1962, Ser. No. 209,876 13 Claims. (Cl. 32389) Devices employing fluid as a working medium are widely used in process control and data handling systems. Under certain circumstances it is desirable to sense for given conditions in a fluid operated system and transmit the information to a remote location. If the remote location is very far from where the system condition is sensed, the fluid signal is often converted to an electrical signal so that it may be more easily transmitted.

An object of the present invention is to provide a novel transducer means for converting a fluid signal to an electrical signal.

More particularly, an object of the present invention is to provide a magnetic circuit, means responsive to a fluid signal for changing the magnetic characteristics of the circuit, and means for sensing the changed characteristics.

An object of the present inventionis to provide a core of magnetic material having an air gap therein, a fluid conveying means extending through the air gap of the core, a movable element in the fluid conveying means, and a source of fluid for selectively moving the movable element through the fluid conveying means to a position where its rests in the air gap. The movable element is preferably a body of magnetic material so that the reluctance of the magnetic circuit with the movable element in the air gap is many times less than the reluctance of the circuit when the movable element is not in the air gap. A coil may be inductively coupled to the magnetic circuit whereby the change is reluctance is manifested by a change in the inductance of the coil.

A further object of the invention is to provide a core of magnetic material having a hole therein, first and second fluid conveying means connected to the ends of the hole, and a magnetic element of substantially the same size as the hole. The magnetic element is contained in the fluid conveying means and is selectively driven to a first position where it rests within the hole and a second position where it is remote from the hole. Preferably, the hole is larger than the core leg in which it is formed to thus provide a substantial air gap in the magnetic circuit of the core when the magnetic element is in its second position. The reluctance of the magnetic circuit is decreased by moving the magnetic element into the air gap. The change in reluctance of the magnetic circuit may be sensed to vary the operating condition of an electrical circuit.

Other objects of the invention and its mode of operation will become apparent upon consideration of the following description and the accompanying drawings in which:

FIGURE 1 shows a first embodiment of the present invention;

FIGURE 2 illustrates an alternative configuration for the movable element and fluid conveying means of FIG- URE 1;

FIGURE 3 illustrates a further embodiment of the invention; and

FIGURE 4 is a sectional view taken along the line 4-4 of FIGURE 3.

FIGURE 1 illustrates the basic concept of the invention in its simplest form. The transducer comprises a core 1 of a suitable permeable magnetic material, a coil 3 a tube, channel or fluid conveying means 5, and a movable element 7. The fluid conveying means is connected to a source 9 which produces the fluid signals to be converted. Source 9 may, for example, be a fluid amplifier of the type described in US. Patent No. 3,001,698. The ball or spherical element 7 is somewhat smaller than the inner diameter of the tube and is free to move vertically therein. Retaining means such as stop pins 11 and 13 are provided to limit the travel of the ball.

The channel extends through the air gap in the core and the stop pin 13 is located such that in its upward extent of travel the ball rests against the pin and between the core faces of the air gap. Preferably, the ball is made of a magnetic material in order to obtain the greatest effect but'non-magnetic materials may be used.

In the normal or no-signal condition the ball 7 rests against stop 11 thus leaving a substantial air gap in the magnetic circuit of the core. When source 9 generates a fluid signal fluid flows upward in tube 5 thus driving ball 7 to its upward extent of travel where it rests in the air gap. Since the inductance (L) of coil 3 is a function of the permeability (a) of the magnetic circuit according to the equation L=K,u where K is a constant dependent upon the area and length of the magnetic circuit, the insertion of the ball having a relatively high ,u. into the air gap having a permeability value ,u l greatly increases the inductance of the coil.

This change in inductance may be utilized in many ways to influence the operation of an electrical circuit. For example, the utilization circuit 15 may contain a tuned amplifier which is selectively tuned and detuned as the ball 7 is selectively moved from its upper limit of travel to its lower limit of travel.

The ball may be returned to its original position against pin 11 by a fluid reset signal applied to tube 5 as indicated by arrow 17. This is particularly desirable in those cases where the tube extends horizontally through the air gap.

FIGURE 2 illustrates a modification of the transducer shown in FIGURE 1 with corresponding parts bearing the same reference numeral. In this embodiment the tube 5 extends through the air gap of the core 1 and divides into two branches 5a and 5b. A portion of tube 5 is cut away to show a right cylinder 19 which may be used in place of ball 7.

The modified device shown in FIGURE 2 functions in essentially the same manner as the device shown in FIG- URE 1. The cylinder 19 normally rests against pin 11 but when fluid is applied to tube 5 in the direction indicated by vector 6 the cylinder moves to the position shown where it rests between the legs of core 1. However, when the fluid stops flowing in channel 5 the cylinder drops downwardly under the force of gravity and rests against pin 11.

FIGURES 3 and 4 illustrate a preferred embodiment of the invention for obtaining a maximum change in the reluctance of a magnetic circuit. A core 1 is made of a magnetic material such as ferrite which can be precisely molded or machined. An aperture such as a cylindrical hole 20 having a diameter D is drilled or otherwise formed in one leg of the core. For maximum effect the diameter D is made somewhat greater than the Width W of the core leg so that there is an air gap of length X between the segments of the core leg. A suitable non-magnetic supporting material 21 is provided to strengthen the core leg and, if the diameter of the hole is greater than width W the supporting material may also serve to seal or make the hole fluid tight. Thus, as shown in FIGURES 3 and 4 the wall of hole 20 has two sections of supporting material and two sections formed by the faces of the core leg. A pair of tubes 50 and 5d each having an inside diameter equal to that of the hole in the core leg are connected to the core to form a continuous fluid passageway from tube 50, through the hole in the core and through tube 5d. A fluid-tight joint between the tubes and the aisaa'zo core may be obtained by using an epoxy bonding resin or another bonding or sealing material at the joints 23. A movable element such as cylinder 19 is located in tube 5c and is free to move in a horizontal direction between stops 11 and 13 in response to fluid pressure exerted against its end surfaces. The tubes 50 and 5d may, by way of example, be connected to the output tubes of a fluid amplifier so that the cylinder is driven from one limit of travel to the other each time the power stream of the amplifier changes its path of flow. Other sources of fluid signals are equally suitable for use with the present invention.

The effect of inserting cylinder 19 into hole 20 may best be illustrated by the following example. Assume that core 1 has a cross-sectional area A, the total effective length of the magnetic circuit including the core and air gap is l, and the air gap created by the hole has an effective length of .11. Assume further that the permeability of the core material is 2000. The permeability of air is of course 1.

The total reluctance of the magnetic circuit is th reinstance of the core plus the reluctance of the hole and may be expressed by the equation R=.9l/2000A +.1 l/1A. This reduces to give the value R=200.9l/2000A. Thus, the total reluctance of the mangetic circuit with cylinder 19 outside the hole as shown in FIGURE 4 is R=200.9I/ 2000A.

Assume now that a fluid signal in channel 50 moves cylinder 19 to the right until it reaches stop pin 13 and rests in the hole. Assume also that the cylinder is made of the same material as the core and thus has a permeability of 2000. The total reluctance of the magnetic circuit is now R=.9l/20QOA+.1l/2000A=l/2000A. Therefore, the reluctance of the magnetic circuit is approximately 200 times greater when cylinder 19 is against pin 11 than when the cylinder is against pin 13,.

It is well known that the flux resulting from an applied magnetomotive force is inversely proportional to the reluctance of the magnetic circuit. The relationship may be expresed by the equation Therefore, it follows that the flux and flux density in core 1 may be varied by selectively inserting and removing cylinder 19 from the hole in response to fluid input signals applied to tubes 50 and 50!.

FIGURE 3 shows one manner in which the present invention may be utilized to produce electrical output signals in response to fluid input signals. The core 1 represents the saturable core of a magnetic amplifier. A bias control winding 25 is connected through a resistance 26 to a voltage source 27 which supplies a DC. control voltage.

A gating Winding 29 is connected in series with a load resistor 31 and a rectifier 33. A voltage source 35 applies an A.C. voltage to the series circuit.

It will be recognized by those skilled in the art that with the exception of cylinder 19 and hole 20 the de- ,vice shown in FIGURE 3 is a conventional single-core, single-rectifier magnetic amplifier circuit. Assume for the moment that hole 20 does not exist. That is, a fluid signal applied to channel 50 has moved element 19 into the hole 20. The magnetic amplifier functions as follows.

At the beginning of a cycle the flux density in the core resulting from voltage source 27 is some value B. As the A.C. source voltage becomes positive rectifier 33 begins to conduct. The load current through the load resistor 31 is substantially zero since the core represents an infinite impedance at this time. The source voltage ap pears across winding 29 thus causing the flux density in the core to increase from B to some value l-B. When the value +B reaches the value. +13 the saturation flux density of the core, the core no longer provides an impedance in the series circuit and the AC. voltage appears across load resistance 31. A load current deter mined by the value of the AC. voltage and the load resistance flows through the resistor 31 until the AC. voltage reaches a zero value. At this time the bias voltage 2'7 acting through winding 25 decreases the flux density in the core until it again reaches the value B. This cycle of operation is repeated as long as element 19 is in hole 2&9.

As described in the preceding paragraph load current flows in resistor 31 only as long as the core is saturated. Stated differently, load current flows only as long as the flux density resulting from the magnetomotive force produced by the AC. signal source is as great as the saturation flux density. As shown previously, the flux or flux density can be reduced by a large factor by providing an air gap in the core.

Therefore, the AC. voltage 35 is preferably chosen such that the magnetomotive force developed by winding 29 as a result of current flowing through it is suflicient to produce a saturation flux density when element 19 is in the hole and the reluctance of the magnetic circuit is low but the magnetomotive force developed by winding 29 is insuificient to produce a saturating flux density when element 19 is not in the hole and the reluctance of the magnetic circuit is high.

In the latter case, the bias voltage initially produces a flux density B in the core. When the AC. voltage goes positive the flux density increases to some value +13 but because of the value of the AC. voltage the value +B is less than the saturation flux density +B As a result, the entire voltage from source 35 appears across winding 29 and a voltage never appears across resistor 31. When the A.C. voltage goes negative bias voltage 27 decreases the flux density to the initial value -B. Thus, with element 19 out of hole 20 an output signal is never developed across resistor 31.

It will be understood that the specific values used herein are for purposes of illustration only and should not be interpreted as limitations on the invention. Furthermore, it will be obvious to those skilled in the art that various modifications and substitutions in the embodiments illustrated may be made without departing from the spirit and scope of the invention. It is intended therefore to be limited only by the scope of the appended claims.

I claim:

1. Means for varying the inductance of a coil, said means comprising: signal generating means for selectively producing first and second fluid signals; magnetic circuit means having an air gap therein, said coil being inductively coupled to said magnetic circuit; fluid conveying means extending through said air gap and having first and second inputs connected to said signal generating means for receiving said first and second fluid signals; and movable means disposed within said fluid conveying means and movable into and out of said air gap in response to said first and second fluid signals.

2. Inductance varying means as claimed in claim 1 and further comprising: first limit means for stopping said movable element in said air gap when it moves in response to said first signal, and second limit means for stopping said movable element at a point remote from said air gap when it moves in response to said second signals.

3. Inductance varying means as claimed in claim 2 wherein said movable means is a movable magnetic element and said magnetic circuit means comprises a core of permeable magnetic material.

4. A fluid to electrical signal transducer comprising: a magnetic core having an aperture in one portion thereof whereby said core provides a high reluctance flux path; means for selectively producing first and second fluid signals; fluid conveying means extending through said aperture and having first and second inputs for receiving said first and second fluid signals; a movable element disposed within said fluid conveying means and selectively movable in response to said fluid signals between a first position outside of said aperture and a second position within said aperture; and sensing means inductively coupled to said core means.

5. A fluid to electrical signal transducer comprising: a magnetic core having an aperture in one portion thereof; first and second fluid conveying means abutting said core and forming with said aperture a continuous path for fluid flow; signal producing means for producing first and second fluid signals, said first and second fluid conveying means being connected to said signal producing means to receive said first and second fluid signals, respectively; a movable element disposed within said continuous path and selectively movable in response to said fluid signals between a first position within one of said fluid conveying 'means and a second position within said aperture; stop means for stopping said movable element at each of said positions; and sensing means inductively coupled to said core.

6. A fluid to electrical transducer as claimed in claim 5 wherein the specific gravity of said movable element is greater than the specific gravity of said fluid.

7. A fluid to electrical signal transducer as claimed in claim 5 wherein the permeability of said movable element is much greater than the permeability of air whereby the reluctance of said flux path is reduced and flux increased when said movable element is positioned in said aperture.

8. A fluid to electrical signal transducer as claimed in claim 5 and further comprising means for structurally supporting the portion of said core in the region adjacent said aperture.

9. A fluid to electrical signal transducer as claimed in claim 8 wherein said aperture forms an air gap in said core.

10. A fluid to electrical signal transducer as claimed in claim 5 wherein said movable element is a movable body of permeable magnetic material and said core is made of a magnetic material having a substantially rectangular hysteresis loop.

11. A fluid to electrical signal transducer as claimed in claim 10 and further including means for applying to said core a magnetomotive force of suificient magnitude to saturate said core when said movable element is in said aperture.

12. A fluid to electrical signal transducer comprising a magnetic core having an aperture in one portion thereof; a source for intermittently emitting fluid signals; means defining a path for fluid flow from said source through said aperture; a movable element the specific gravity of which is greater than the specific gravity of said fluid, said element being disposed within said path defining means and movable to a position in said aperture in response to fluid flowing from said source; means for stopping said movable element in said aperture; and sensing means coupled to said core.

13. A fluid to electrical signal transducer as claimed in claim 12 wherein said means defining a path for fluid flow is vertically disposed at least along the path of said movable element; and further stop means for limiting the movement of said element when said source does not emit fluid.

References Cited by the Examiner UNITED STATES PATENTS 2,120,048 6/38 Turner 336-30 X 2,979,959 4/61 Clurnian 336-30X JOHN F. BURNS, Primary Examiner. 

12. A FLUID TO ELECTRICAL SIGNAL TRANSDUCER COMPRISING A MAGNETIC CORE HAVING AN APERTURE IN ONE PORTION THEREOF; A SOURCE FOR INTERMITTENTLY EMITTING FLUID SIGNALS; MEANS DEFINING A PATH FOR FLUID FLOW FROM SAID SOURCE THROUGH SAID APERTURE; A MOVABLE ELEMENT THE SPECIFIC GRAVITY OF WHICH IS GREATER THAN THE SPECIFIC GRAVITY OF SAID FLUID, SAID ELEMENT BEING DISPOSED WITHIN SAID PATH DEFINING MEANS AND MOVABLE TO A POSITION IN SAID APERTURE IN RESPONSE TO FLUID FLOW FROM SAID SOURCE; MEANS FOR STOPPING SAID MOVABLE ELEMENT IN SAID APERTURE; AND SENSING MEANS COUPLED TO SAID CORE. 